1. Field of the Invention
The present invention relates to a white balance control device of a video camera, particularly to a white balance control device for properly controlling white balance by a method of inside light measurement.
The invention further relates to a white balance control device for properly controlling white balance by a method of inside light measurement and a method of divided scope light measurement, and a white balance control device for reducing the occurrence of color failure when photographing under artificial light and natural light.
The invention further relates to a video camera for reproducing proper colors of an object when photographed under a fluorescent lamp and a video camera for photographing an object illuminated by a fluorescent lamp which prevents flicker from occurring.
2. Related Art
In conventional video cameras and video still cameras, a white balance control is utilized in order to reproduce a white object as a white colored material. The white balance control is operated by controlling a gain of a red signal circuit and a gain of a blue signal circuit in the camera based on a green signal as a reference value.
In the white balance control, it is necessary to measure a tint (color temperature) of a photographing working field for operating the white balance control. As methods of the white balance control, there are an outside light measuring method and an inside light measuring method, which are different from each other in measuring the color temperature of the photographing working field.
In the outside light measuring method, a color temperature is directly detected by a color temperature sensor. A white balance control signal for a red signal and a white balance control signal for a blue signal are produced based on reference data detected by the color temperature sensor in order to control the white balance. The color temperature sensor is integrally formed with photo sensors, for example, a photo sensor with a red filter, a photo sensor with a green filter and a photo sensor with a blue filter. The white balance control signal for the red signal and the white balance control for the blue signal are produced by an output voltage of each photo sensor, respectively.
On the other hand, in the inside light measuring method, a color temperature is indirectly detected by a color temperature sensor. If a white balance is matching in a picture, an averaged color of whole colors in a picture an becomes achromatic color (grey). The inside light measuring method utilizes this theory That is, an integrated averaged value of color difference signals R-Y and B-Y at a reference color temperature that an averaged color for all of the colors in a picture becomes an achromatic color is designated as a reference value for each signal. Values of the red signal and the blue signal are feed back controlled in order to match the integrated averaged value with the reference value.